Following London in 2007 i've tried to do a different one each year. Doing it on a budget is essential, so Selection is mainly down to availability of cheap flights and hotels.
Edinburgh: Good, but organisation from finish line was a joke, so wouldn't do again, or recommend. This may have changed since 2008.
Palma, Majorca: Well organised race, nice route and good weather.
Budapest: Excellent course and organisation, very cheap flights and accomodation. Would recommend for race abroad
Barcelona: Excellent! City, atmosphere and route unbelievable. This is head and shoulders my favourite race. Cant recommend it highly enough.
Palma and Budapest are September time, whilst Barcelona March.